Mixed-up socks poster

With three pairs of socks, there is only one way to do it. For example, if there is a pair of red socks, a pair of blue socks and a pair of green socks , the mixed-up pairs are:

red blue

red green

blue green

If you have four pairs (for example, a pair of yellow socks), there are three ways:

red blue

red green

blue yellow

green yellow

or

red blue

red yellow

blue green

green yellow

or

red green

red yellow

blue green

blue yellow